Comparison of three wet-alkaline methods of digestion of biogenic silica in water

Methods for determination of low levels of biogenic silica (0.2–0.4 mg SiO 2 ) in aqueous samples after digestion with three wetalkaline extraction procedures compared favourably in both precision of replicates and recovery of silica utilized by diatoms in budgeted cultures. Leaching samples with 0.2 M NaOH for 10–15 min at 100°C was the least time consuming procedure. Also interference from silicate minerals was lower for this method than leaching with either 0.5 or 5% Na 2 CO 3 for 2 h at 85°C. The use of filters to concentrate samples enables detection of low levels of biogenic silica with colorimetric procedures. Polycarbonate filters are recommended in preference to cellulose acetate or polyvinyl chloride filters for sample collection. Time-course experiments are recommended for establishing digestion times and determining the presence of mineral silicate interference. Wet-alkaline digestion methods are recommended for routine analysis of biogenic silica in suspended matter in preference to infra-red analysis, alkaline fusion and hydrofluoric acid/nitric acid methods.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74725/1/j.1365-2427.1983.tb00658.x.pd

Decay spectroscopy at the two-proton drip line: radioactivity of the new nuclides 160Os and 156W

The radioactivity of 76160Os84 and 74156W82 that lie at the two-proton drip line have been measured in an experiment performed at the Accelerator Laboratory of the University of Jyväskylä. The 160Os nuclei were produced using fusion-evaporation reactions induced by a beam of 310 MeV 58Ni ions bombarding a 106Cd target. The 160Os ions were separated in flight using the recoil separator MARA and implanted into a double-sided silicon strip detector, which was used to measure their decays. The α decays of the ground state of 160Os (Eα = 7092(15) keV, t1/2 = 97−32+97 μs) and its isomeric state (Eα = 8890(10) keV, t1/2 = 41−9+15 μs) were measured, allowing the excitation energy of the isomer to be determined as 1844(18) keV. These α-decay properties and the excitation energy of the isomer are compared with systematics. The α decays were correlated with subsequent decays to investigate the β decays of the ground state of 156W, revealing that unlike its isotones, both low-lying isomers were populated in its daughter nuclide, 156Ta. An improved value for the half-life of the proton-decaying high-spin isomeric state in 73156Ta83 of 333−22+25 ms was obtained in a separate experiment using the same experimental systems with a 102Pd target. This result was employed to improve the precision of the half-life determined for 156W, which was measured as 157−34+57 ms